BALTIMORE (WJZ) — A delicate balance must be struck when it comes to the intake of folate and B12 by pregnant women, according to new research from the Johns Hopkins Bloomberg School of Public Health.

Doctors tell women who plan on becoming pregnant that they need enough of folate to ensure proper fetal neurodevelopment, but having too much could carry serious risks, as well, a new study shows.

For the study, researchers analyzed data from 1,391 pairs of mothers and children in the Boston Birth Cohort. The mothers were recruited at the time of their child’s birth — between 1998 and 2013 — and followed for several years, with the mother’s blood folate levels checked once within the first one to three days of delivery.

Researchers found that if a new mother has a very high level of folate right after giving birth – more than four times what is considered adequate – the risk that her child will develop an autism spectrum disorder doubles.

Folate is found naturally in fruits and vegetables and the synthetic version, folic acid, is in vitamin supplements and used to fortify cereals and breads in the U.S.

Very high vitamin B12 levels in new moms are also potentially harmful, tripling the risk that her baby will develop an autism spectrum disorder.

If both B12 and folate levels are extremely high, the risk that a child develops the disorder increases 17.6 times.

The researchers found that one in 10 of the women had what is considered an excess amount of folate and six percent had an excess amount of vitamin B12.

A large majority of the mothers in the study reported having taken multivitamins – which would include both nutrients – throughout pregnancy.

But the researchers say they don’t know exactly why some of the women retained such high levels in their blood.

It could be that they consumed too many folic acid-fortified foods, took too many supplements, or that some women are genetically predisposed to absorbing greater quantities of folate or metabolizing it slower. It could also be a combination of the factors.

With many types of vitamin supplements, conventional wisdom has been that the body will flush out the excess. That may not be the case with these nutrients.

More research is needed, the scientists say, in order to determine just how much folic acid and B12 a woman should consume during pregnancy to have the best chance of ensuring her baby’s health.

“We have long known that a folate deficiency in pregnant mothers is detrimental to her child’s development,” says one of the study’s senior authors M. Daniele Fallin, PhD, director of the Bloomberg School’s Wendy Klag Center for Autism and Developmental Disabilities.

“But what this tells us is that excessive amounts may also cause harm. We must aim for optimal levels of this important nutrient.”

The findings will be presented May 13 at the 2016 International Meeting for Autism Research in Baltimore.

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